The present invention concerns a height-measuring column. The present invention concerns also the method for regulating a height-measuring column according to the invention.
Height-measuring columns are measuring machines enabling the height of a point relative to a reference plane to be measured or the vertical distance between to measuring points to be calculated. The precision that is expected of such measuring machines is on the order of the micron.
The main elements of a height-measuring column are generally:
a base;
a supporting frame;
a carriage;
a probe tip;
a measuring system;
a driving mechanism.
The base is the element through which the height-measuring column is in contact with the floor, generally a plane surface that can serve as reference to the measuring reference frame. The base also ensures the stability of the height-measuring column.
The supporting frame is essentially perpendicular to the base""s seat and generally has on its length rails guiding the displacement of the carriage. It thus determines the measuring axis, essentially perpendicular to the plane of the base""s seat of the height-measuring column.
The carriage is the mobile element of the height-measuring column. It moves on the supporting frame along the measuring axis, generally on perfectly rectilinear rails guiding its movement and ensuring that it is fastened.
The probe tip is mounted on the carriage and is designed for being brought into contact with the piece to be measured. The contact point is determined either visually, or automatically, for example by a mechanism stopping the carriage""s movement as soon as a pressure exceeding a predetermined threshold is exerted on the probe tip. The height of the contact point can then be measured.
The measuring system comprises elements for example inductive, capacitive or opto-electronic integrated to the supporting frame, enabling the carriage""s position along the measuring axis to be determined accurately. The measuring system is generally equipped with a system for displaying the measure and/or with an information processing software.
The driving mechanism controls the displacement of the carriage on the supporting frame. It is generally an electric motor driving a belt or cable fastened to the carriage and guided by a pulley at the top and sometimes at the bottom of the supporting frame. The driving mechanism has mechanical and/or electronic controls enabling an accurate positioning of the carriage and therefore of the probe tip.
In order to guarantee the accuracy of the height measuring, it is important that the measuring axis be perpendicular to the reference surface. However, possible measuring errors caused by a slight inaccuracy of this parameter are small, so that this perpendicularity is rarely ideal in the prior art height-measuring columns. Furthermore, many columns have a electronic correction circuit, enabling the linear measuring error on the vertical axis caused by a non-perpendicularity to be compensated, the correction circuit being calibrated at manufacture by comparison with a standard gauge measure. A correction of the measuring in workshops is however difficult, as most of the workshops do not have the required standard gauge measures.
However, a height-measuring column can also be used for perpendicular measuring. The probe tip can in this case be replaced by a comparator that is displaced flush along a surface of the piece to be measured, detecting any variation in the distance between the surface to be measured and the displacement axis of the comparator. For such an application, the perpendicularity between the measuring axis and the reference surface becomes the essential factor of the measuring accuracy. This perpendicularity must consequently be perfectly regulated. An electronic correction circuit is superfluous, since the information supplied by the comparator is binary.
There are measuring columns whose perpendicularity between the supporting frame and the base""s seat is guaranteed by the manufacturing precision of these elements. The contact surfaces between the base and the supporting frame are manufactured with the greatest precision, ensuring a perfect assembly. The base""s seat must also be perfectly plane to give the supporting frame a position perfectly perpendicular relative to the reference surface. A variant embodiment uses the upper part of the base as reference surface and in that case, it is the later that must be manufactured with the greatest precision. Whichever option is chosen, such a manufacture is costly and complicated since both the quality of the manufacturing of the pieces and their assembly must be performed with the greatest care. Furthermore, since the resting length of the piece to be measured on the base or on the reference surface is smaller than the column""s height, any manufacturing imprecision being further amplified at the level of the resulting perpendicularity.
Other measuring columns have a base whose seat can be regulated, thus enabling the parallelism between the base and the reference surface to be regulated. These systems are usually realized by means of adjustable feet. These solutions are also rather costly since they involve a certain complexity in the manufacturing of the base. Furthermore, such a mechanism is not very stable through time and its setting must be controlled frequently.
It is an aim of the present invention to propose an easy and sturdy way of regulating the perpendicularity between the measuring axis of a height-measuring column and the work surface.
According to the invention, this aim is achieved by means of a measuring column having the characteristics of the first independent claim. This aim is further achieved by means of a regulating method indicated in the second independent claim.
In particular, this aim is achieved by means of a height-measuring column whose perpendicularity between the supporting frame and the base can be regulated, thus allowing by extension the perpendicularity of the measuring axis relative to the reference surface to be regulated.
The regulating of the perpendicularity between the supporting frame and the base of the height-measuring column makes it possible to compensate the inaccuracies in the parallelism or in the regularity of the contact surfaces between the different elements of the height-measuring column, in particular between the supporting frame and the base. Thus, the manufacture of these pieces is simplified and the costs are reduced.